Process for refining airplane engine oil



can treat oils from mixed base crudes to subtreats on the viscosity-temperature 'coefiicient of Patented Nov. 13, I934 UNITED STATES PATENT OFFICE PROCESS FOR REFINING AIRPLANE ENGINE OIL Arthur B. Brown and Arthur W. Neeley, Whiting,

Ind., assignors to Standard Oil Company (Indiana), Chicago, 111., a corporation of Indiana No Drawing. Application September 12, 1930,

Serial No. 481,594

10 Claims. (01. 196-44) This invention relates to a process of making be prepared by vacuum distillation, pipe-still disimproved lubricating oils and especially high tillation or other well-known method. When viscosity lubricating oils suitable for airplane enemploying such a distillate in our process we obgine lubrication. Because of the high temperatain higher yields of finished oil with a sometures at which airplane engines operate, it is What lower chemical requirement than when renecessary to provide a lubricating oil of high sidual oils are employed. viscosity at ordinary temperatures and, in par- Having such an oil as a starting material, it is ticular, one which will retain its viscosity at high next subjected to a vigorous treatment with sultemperatures. For this work, oils having a visfuric acid. For this purpose we prefer to use cosity of between 90 and 150 seconds Saybolt at fuming sulfuric acid oi about 104.5% H2SO4 210 F. are ordinarily employed. Furthermore, grade. We have found, however, that lower acid these oils must be abnormally stable to oxidation concentrations may be employed with advantage and sludging if they are to give satisfactory for the first part of the treatment, if the treatservice under the severe conditions to which they ing is finished with fuming acid. Thus, We may are sub ected, treat the oil first with 93% H2SO4 and finally 7 The object of this invention is to provide a with 104.5% H2804. With the weaker acid, we mineral 'lubricating oil which will retain its have found it advantageous to carry out the viscosity to a greater extent than any oil heretreatment at elevated temperature and a temtofore used for airplane lubrication, and further, perature of 180 F. has been found satisfactory. to provide an airplane lubricating oil which will At this temperature, less acid may be used to not be subject to sludging even after prolonged obtain the same treating effect. With acid of use at high temperatures. Another object of the this strength, however, there is a practical limit invention is to provide an airplane lubricating to the degree to which the viscosity-temperature oil having an extremely low content of non-comcoefficient can be reduced. Beyond that, it is 25 bustible ash. necessary to use stronger acid and preferably All lubricating oils are characterized by a refuming acid. duction of viscosity with increase in temperature In our preferred procedure we subject the oil and some oils suffer a much greater loss of visto a succession of acid treats as above, making a cosity with increase in temperature than do separation of the treated oil from sludge followothers. In general, oils made from paraffin base ing each treat. A convenient quantity of acid crudes suffer the least change in viscosity with to use in each treat is about one half pound per temperature, and are said to possess a low visgallon of oil. Because of the high viscosity of the cosity-temperature coefficient, whereas oils made oil it is necessary to employ a suitable diluent, from asphalt base crudes sufier the greatest and for this purpose we have found it convenient 35 change of viscosity with temperature, and are to use a gas oil or kerosene stock prepared from said to possess a high viscosity-temperature 00- straight distillation of Mid-Continent crude oil. eificient- 0 8 made om m d ba crudes 00- This diluent is subsequently removed from the oil py an intermediate position by distillation after the chemical process has been We have now discovered a method by Wh c W completed. The effect of the succession of acid sta t a y lower their viscosity-temperature the oil is well illustrated by the following table efiicient- In fact, We have been able y using 0111' which shows the ratio of Saybolt viscosity at method to reduce he vi i yp F. to viscosity at 210 F. for an oil of 120 seconds efficient of mixed base lubricating oils to that of s b lt Viscosity at made by treating 38% parafiln base oils and even lower. Likewise, our M Q residuum with one pound of fuming acid 100 process may be applied to paraffin base lubricatper gallon in Successive treats: ing oils for the preparation of oils having a still lower viscosity-temperature coefficient.

In carrying out our invention we prefer to use Number Viscosity 50 as starting materials oils of high viscosity, as, treats for example, a 38% residuum from Mid-Continent crude. We may also employ a high visg cosity distillate from Mid-Continent crude, preferably one having a viscosity between 150 and 300 5 seconds Saybolt at 210 F. Such a distillate may The significance of these figures will be made apparent when compared with the viscosity ratio, 13.3, of a lubricating oil with a viscosity of 120 seconds Saybolt at 210 F. derived from paraffin base crude by the usual refining methods. We have found that oils most suitable for airplane engine lubrication should have a viscosity ratio of less than 15 and a Saybolt viscosity of 110-130 seconds at 210 F.

Although the oils prepared in the above man ner are satisfactory from the standpoint of viscosity, it is difficult to refine them to acceptable ash content since they possess prohibitive quantitles of oil soluble acids such as sulfonic acids and other sulfuric acid derivatives, which, on neutralization, are converted into oil soluble soaps. These soaps are extremely diffi'cult to remove from the viscous oil and, in fact, cannot be removed by any of the common methods such as extraction with alkalis, alcohol, etc. After neutralization and alcoholic extraction, for example, these oils will contain sufi'icient soap to leave a non-combustible residue of from 0.5 to 1.3%. We

have discovered that these refractory sulfonic I acids and soaps can be successfully removed by subjecting the oil to treatment with anhydrous aluminum chloride subsequent to the acid treatments above described. Although aluminum chloride, has previously been used for treating hydrocarbon oils, we believe we are the first to discover its unusual affinity for sulfonic acids. In addition to removing the sulfonic and other objectionable organic acids, the aluminum chloride also assists in reducing the'viscosity-temperaturecoefficient of the oil.

Inusing aluminum chloride, precautions must betaken to prevent access of water. If the oil is neutralized after the sulfuric acid treatment, it should be carefully dried for the subsequent aluminum chloride treats. In our preferred method, we do not neutralize the oil after sulfuric acid treating but after separating from the acid sludge we apply the aluminum chloride directly to the sour oil. The aluminum chlorideis preferably applied in a succession of treats, and

quantities of 0.3 pound'per gallon of sour oil have beenfound suitable. One, such treat is sufficient to reduce the ash from 0.8% to about 0.04%, and twosuch treats will reduce the ashv to about 0.01%. The aluminum chloride treats may suitably be carried out at a temperature of 200 to 300 F. Somewhat lower temperatures may be employed but we avoid temperatures above 400 F; because of excessive cracking.

After the aluminum chloride treating, the oil is separated from the sludge, neutralized inthe. usual manner and dewaxed. The diluent may then be removed by distillation and the oil'finally finished by treating it with a, small quantity of fullers earth. 0r after separation from the aluminum chloride sludge, the oil may be treated with fullers earth to obtain more complete sludge separation, thereafter neutralized, dewaxed and distilled to remove diluent. Either method yields an oil of high viscosity and negligible ash content which is remarkable for its excellent color, low viscosity-temperature coefficient and freedom from asphaltic constituents. Distillation may be carried out by use of vacuum, steam or other well known method. to produce oils of the desired viscosity, either as bottom stocks or as overhead cuts. Wax may be removed by any of the usual methods either before or subsequent to removal of diluent.

The following example will illustrate the procacid per gallon of distillate.

ess which is the subject of this invention as carried out on the large scale:

19,600 gallons of a distillate from Mid-Conth nentcrude oil having a viscosity of 234 seconds Saybolt at 210F. were diluted with 8,400 gallons of gas oil distillate. The mixture was then treated with one pound of 93% acid per gallon applied in two lots of one-half pound per gallon each, the sludge being separated after each treatment. The oil was then given two successive treats of one-half pound each of 104.5% fuming sulfuric After the final acid sludge separation there remained 17,500 gallons of sour oil mixture. This oil was then treated with two successive lots of aluminum chloride of 0.4 pounds each per gallon of sour oil mixture at a temperature of 250 F. From four to eight hours were required for each treat, agitating the oil continuously during this time. The sludge was removed after each treatment and the oil was finally neutralized with caustic and distilled to the proper viscosity. The finished oil had a viscosity after dewaxing of 120 seconds at 210? F. and a Viscosity ratio of 13.8. The color after treating with a small amount of fullers, earth was a pale fluorescent yellow and the ash content was 0.01%, Whereas the ash content of the oil before the aluminum chloride treat was about 1%. This oil was tested in airplane engines and found to be superior to any oil previously employed, particularly from the standpoint of sustained viscosity and of freedom from sludge deposition, in the crankcase and on the working parts of the engine.

After running for fifty hours with a jacket temperature of BOO-350 F. and a crankcase temperature of 220-250 F., the Viscosity of the oil which was originally 114 sec. Saybolt at 210 F. remained entirely unchanged showing, no sludge'formation nor polymerization by the high temperature. A standard, paraffin base oil subjected tothe same test increased in, viscosity from 125 to 136 sec. at 210 F., and a standard mixed base airplane oil Went from 126 to, 186 sec. at 210 The latter oil developed an acidity three times that of our improved airplane oil and nearly twice the amount of insoluble sludge, the sludge formation being lower with our improved oil than'with any other oil tested.

From the results of these and other tests, we believe we have discovered a method of making from mixed base crudes, lubricating oils with viscosity ratios substantially equivalent to those for paraffin base oils but with a degree of stability in airplane engine service surpassing that of any other oil known.

We have described our improved process in con;

nection with a specific example thereof, but do not intend that it be limited thereby except, as set forth in the following claims.

We claim: 1

1. The process of producing ash-free lubricate ing oils of low viscosity-temperature coefiicient comprising subjecting a viscous lubricating oil admixed with a suitable diluent to a treatment with concentrated sulfuric acidsufficient to substantially reduce its viscosity-temperature coefficient and form undesirable sulfonic acids in the oil, separating the oil containing said sulfonic acids from the resulting acid sludge, then treating with anhydrous aluminum chloride in quantity surficient to remove substantiallyall sulfonic acids present inthe oil, separatingthe aluminum chlar-ide sludge and. neutralizing the oil.

2, Theprocess of producing ash-free lubricat.

ing oils of low viscosity-temperature coefiicient from mixed base crudes comprising distilling the crude toproduce a viscous lubricating oil, subjecting the viscous oil admixed with a suitable diluent to a treatment with concentrated sulfuric acid sufficient to substantially reduce its viscosity-temperature coefiicient and form undesirable sulfonic acids in the oil, separating the oil containing said sulfonic acids from the resulting acid sludge, then treating the oil with anhydrous aluminum chloride in quantity sufficient to remove substantially all sulfonic acids present in the oil, separating the aluminum chloride sludge and finally finishing the oil by neutralizing, dewaxing, and distilling to the desired viscosity.

3. The method of reducing the viscosity-temperature coefiicient of viscous mineral lubricating oils comprising subjecting said oils to a treatment with fuming sulfuric acid, separating the oil from the acid sludge, then treating the oil with anhydrous aluminum chloride and neutralizing the resulting oil.

4. The process according to claim 3 wherein the viscous lubricating oil employed is a crude oil residue.

5. The method of reducing the viscosity-temperature coeflicient of viscous mineral lubricating oils comprising subjecting the oil to a succession of fuming sulfuric acid treats, separating the oil after each treat from the acid sludge, then treating the oil after the final acid treat with anhydrous aluminum chloride and neutralizing the resulting oil.

6. The process of reducing the viscosity-temperature coefficient of viscous mineral lubricating oils comprising successively treating with 93 to 100% sulfuric acid at a temperature above 160 F. then treating with fuming sulfuric acid, separating the acid sludge after each successive treat and then treating the oil after the final acid treat with anhydrous aluminum chloride to remove sulfuric acid derivatives and further reduce the viscosity-temperature coefiicient.

7. The method of removing oil-soluble organic acids from sulfuric acid-treated viscous mineral lubricating oils comprising treating the sour oil resulting from the acid treatments directly after removing the sulfuric acid sludge, with suiiicient anhydrous aluminum chloride to remove the said organic acids.

8. The method of removing oil-soluble ashforming sulfuric acid derivatives from viscous mineral lubricating oils having ash contents above 0.5% comprising treating the oil with sufficient anhydrous aluminum chloride to remove said sulfuric acid derivatives whereby the ash content of the oil is substantially reduced.

9. The method of removing oil-soluble ashiorming soaps from viscous mineral lubricating oils containing in excess of 0.5% ash comprising treating the oil with sufiicient anhydrous aluminum chloride to remove said soaps, separating the resulting aluminum chloride sludge and neutralizing the remaining oil.

10. The method of removing from acid treated viscous mineral lubricating oils, oil soluble sulfuric acid compounds incapable of being removed by alcohol extraction, comprising treating the oil with sufficient anhydrous aluminum chloride to remove the said sulfonic acid compounds following the acid treatment and separating the resulting aluminum chloride sludge.

ARTHUR B. BROWN. ARTHUR W. NEELEY. 

